Q.crepe myrtle
I have had my crepe myrtle for approx. 8 yrs. I have always severely pruned it to keep it from becoming too large a tree. It always came back beautifully. This year, it is the middle of June and there is no sign of any life. What did I do??

Severe pruning can be detrimental to tree health, But there are other possible factors. Look to the growing conditions and water management. Was there any soil/root disturbance, trenching, sewer repair, compaction. drought stress, bark damage at the base of the tree from lawn mower or string trimmer?
https://www.gardeningknowhow.com/ornamental/trees/tgen/sudden-tree-death-causes.htm